Food allergy affects approximately 6 to 8 percent of young children and 3 to 4 percent of adults in the United States, and is the single leading cause of life-threatening anaphylactic reactions treated in hospital emergency departments. Food hypersensitivity in general is thought to result from a defect in either the induction or maintenance of oral tolerance. The mechanisms underlying this tolerance, let alone sensitization, have yet to be elucidated. Accordingly, dendritic cells (DC) including monocytoid (mDC) and plasmacytoid (pDC) likely play a key role in this regulation. In particular, most all human DC subtypes thus far described express the high affinity IgE receptor (FceRI), indicating that these APCs function not only in sensitization but also in effector phases of allergic reactions. Our findings have prompted the general hypothesis that IgE/FceRI interactions play an important role in directing DC maturation and function by rwe have described some of these functional changes in immature DCs among adult patients with allergic respiratory tract disorders, but have yet to examine DCs from food allergic patients, including pediatric subjects. Three Aims are proposed. Aim 1 is to characterize immature DC subtypes from the blood of milk allergic subjects, milk allergic subjects who have out grown their disease, and in normal controls. Phenotypic and functional parameters will be investigated with emphasis on whether differences in adaptive vs. innate immune cytokine responses are observed among the DCs from the 3 groups of subjects. Aim 2 will simultaneously correlate DC responses with those from two effector cell types: basophils and CD4+ T-cells. The focus on basophils centers on IgE-dependent histamine release and IL-4 secretion, but also on more novel cytokines including IL-3 and IL-25. DC-dependent allergen- driven cytokines produced by CD4+ lymphocytes will be investigated using multiplexing assays with thhould add significantly to or understanding of how these cells participate in food allergy. Rare cells that are found in blood (i.e. called basophils and dendritic cells) are thought to contribute to the symptoms associated with food allergy and allergies in general. This application outlines experiments that focus on identifying differences in the responses of these white blood cells in children who are allergic to milk verses those from subjects who are no longer allergic to milk. By identifying differences (or biomarkers) that associate with these cells from milk allergic subjects, we might better understand why milk allergy persists and, more importantly, develop new strategies to treat the disease and allergies in general.